Corona treatment of textiles

ABSTRACT

A PROCESS FOR ENCHANCING THE SPINNABLITY OF FIBERS, PARTICULARLY WOOL AND COTTON, WHICH COMPRISES EXPOSING SAID FIBERS TO A CORONA DISCHARGE ZONE FOR THE PURPOSE OF IMPARTING BOTH A TRANSITORY AND A PERMANENT INCREASE IN COHESIVENESS TO SAID FIBERS.

Jun: 18, 1974 w. J. THORSEN comm. TREATMENT OF TEXTILES 2 Sheets-Sheet 1 Filed July so, 1970 L O O W D E m i 0 j E w O R m G J. M E 0 o R O O W O C X D I m E k A X O /P l J Ix j I O O O m G GV womom m wmIO0 TIME AFTER CORONA TREATMENT(Min) CORONA-TREATED COTTON O 8 6 4 2 O 2 2 I I I I l G OV mQmOm m m wIOo IO 20 4O 60 I00 200 400 600 I000 TIME AFTER CORONA TREATMENT (Min) WALTER J. THORSEN INVENTOR HW SK MM ATTORNEYS June 4 w. J. THORSEN ,817,701

conom mmmnm .OF TEXTILES,

Filed July so, 1970 2 Sheets-Sheet z '8 $6M (d; SPINNING YARN aw??? FRAME (PRODUCT) I, I3 I SOURCE GAS POWER SOURCE I 3 WALTER J. THORSEN INVENTOR ATTORNEYS United States Patent 3,817,701 CORONA TREATMENT OF TEXTILES Walter J. Thorsen, El Cerrito, Calif., assignor to the United States of America as represented by the Secretary of Agriculture Continuation-impart of application Ser. No. 861,225, Sept.

19, 1969, now Patent No. 3,632,299, which is a continuation-impart of abandoned application Ser. No. 442,561, Mar. 24, 1965. This application July 30, 1970, Ser. No. 59,398

Int. Cl. B01k 1 00; D06m 3/08 US. Cl. 8-116 R 10 Claims ABSTRACT OF THE DISCLOSURE A process for enhancing the spinnability of fibers, particularly wool and cotton, which comprises exposing said fibers to a corona discharge zone for the purpose of imparting both a transitory and a permanent increase in cohesiveness to said fibers.

This application is a continuation-in-part of my copending application, Ser. No. 861,225, filed Sept. 19, 1969', now Pat. No. 3,632,299 which in turn is a continuation of Ser. No. 442,561, filed Mar. 24, 1965, now abandoned.

A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to and has among its objects the provision of novel processes for modifying textile materials. Further objects of the invention will be evident from the following description and the annexed drawings.

In the drawings:

FIGS. 1 and 2 are graphs illustrating the results achieved in accordance with the invention.

FIG. 3 is a schematic diagram of apparatus for carrying out the process of the invention.

The invention is applicable to textile materials of all kinds such as wool, mohair, and other proteinous fibers; cotton, jute, flax, hemp, and other cellulosic fibers; and synthetic fibers, including rayon, acetate, acrylic, nylon, polyesters, and the like.

The treatment in accordance with the invention yields such technically-important advantages as increase in fiber, yarn, and fabric tensile strength, increase in fiber cohesiveness, and increase in abrasion resistance.

Fibers treated in accordance with the invention exhibit greatly improved spinning properties. Accordingly, spinning may be conducted at increased rate (increased spindle speed) without any increase in ends down or breaks in the yarn per unit of spinning time. As a result, the invention provides the economic advantage that a greater amount of yarn can be produced in a given time than is possible with untreated fibers. This is illustrated by the following example: Wool top treated in accordance with the invention could be spun at a spindle speed of 8,800 r.p.m., whereas with the untreated wool fibers the maximum spindle speed which could be used was only 6000 rpm.

Moreover, yarns with less twist-which makes them softer and hence more desirable-can be produced without sacrificing tensile strength. It may be noted that in normal operations a decrease in twist is accompanied by a reduction in tensile strength.

The invention makes it possible to produce finer, more expensive yarns from fibers of standard diameter or length. Conversely, yarns of good quality can be spun from the cheaper or coarser fibers. Thus, for example, yarns of useful properties can be spun from short fibers, lint, or similar Patented June 18, 1974 lCC materials which are generally regarded as waste or dis count fibers. Another advantage of the invention is that it provides improved blending properties. For example, in conventional procedures wool-cotton blends require longstaple Egyptian cotton to achieve desired yarn strength. By application of the process of the invention, short-fiber cotton can be successfully substituted for longstaple with resulting economic advantages.

A basic step in the practice of the invention is that the textile material is subjected to a corona treatment at atmospheric pressure. Typically, this is done in an apparatus which provides a pair of electrodes open to the atmosphere, and connected to a source of high voltage to cause a corona discharge between the two electrodes. The textile material is passed through the zone where the discharge is taking place with the result that the material is modified as above described. Instrumental in attaining the desired modification are various gases such as ozone generated in situ within the corona cell by the action of the electrical discharge on the air contained in the cell.

Although some investigators have previously advocated the subjection of textile fibers to electrical discharge, it has not previously been realized that there is an important element of time as regards the initiation of mechanical treatments following the corona treatment. I have found that time is of the essence if the full improvement in spinning quality is to be realized. My researches have shown that the corona treatment of textiles imparts two distinct components of modification, hereinafter termed Components A and B. Both of these contribute to improved spinning quality but differ in their degree of permanence and their magnitude. Component A has a transitory nature; its dissipation starts as soon as corona treatment is completed, and is virtually completely dissipated in about 10 to minutes, depending on the type of textile. On the other hand, Component B is permanent-it remains for the life of the treated fibers. From the standpoint of magnitude, Component A is the larger. Although Component A has an effect of larger magnitude than Component B, its presence was not previously noticed because of its transitory nature. With conventional systems, wherein no heed is paid to the time factor, the effect of Component A is simply not observedby the time the coronatreated fibers are tested with instruments or otherwise evaluated, the eifect of Component A has been dissipated and only the permanent effect of Component B remained to be measured and observed. In contrast, the invention not only involves the recognition of the time-dependent characteristic of Component A, but also utilizes it to obtain advantages heretofore unattainable. This is typically accomplished as follows: Textile fibers, for example in the form of rovings, are passed through the corona cell and then within a brief period of time are subjected to conventional spinning operations to make yarns. In this way, the fibers being spun still retain both components whereby one realizes an extra bonus of spinning quality improvement. In other words, one utilizes not only the permanent improvement in spinning quality (Component B) but also the transitory improvement in spinning quality (Component A) which was never recognized heretofore and which was not utilized heretofore because prior investigators were unaware of the need for applying spinning without delay after the corona treatment.

The nature of Components A and B and their characteristics are illustrated by the following experiments.

EXPERIMENT I Wool roving (2-grain) was treated for 31 seconds in a corona cell exposed to ambient air, 15 kv., 60 Hz. at C. After this treatment the roving was tested for cohesiveness over a period of time. In this test the roving is drawn between two sets of drafting rolls geared for a 1.78 draft. The tension in the roving as it is being drafted is measured by a strain gauge and recorded on a strip chart recorder. The results obtained are shown in FIG. 1 wherein curve 1 represents a graph of cohesive force vs. time after corona treatment. The broken line designated as 2 represents the cohesive force of the untreated roving.

It is evident from FIG. 1 that the cohesive force essentially immediately after treament (about 30 seconds was required to set up the test) was 39 grams. Fifteen minutes later this force had dropped to 34 grams and 85 minutes later to 19 grams. The decay of Component A was essentially complete in about 85-100 minutes. After this, the residual permanent increase in cohesion (Complement B) remained essentially constant at 17 grams. Since the cohesiveness of the untreated roving was 14 grams, the permanent increase in cohesions was 3 grams or 21%. It is also evident from FIG. 1 that where spinning is applied soon after corona treatment, one takes advantage not only of the permanent spinning improvement of 21% but also of the much higher degree of spinning improvement which amounts to approximately a 17% improve ment.

EXPERIMENT 11 Cotton roving (S-grain) was treated at 9095 C. for 2.8 seconds in a corona cell, 15.57 kv., 2070 Hz. The cell was at atmospheric pressure and supplied with a mixture of chlorine and air at the rates of 0.07 s.c.f.m. and 0.35 s.c.f.m., respectively. The treated roving was then tested for cohesiveness as previously described. The results are shown in FIG. 2 wherein curve 3 is a graph of cohesive form vs. time after corona treatment. The untreated roving had a cohesive force of 5.2 grams (not shown in the figure because of its low value).

Essentially immediately after the corona treatment (it took about 60 seconds to set up the test), the cohesive force was 22 grams, a 420% increase above that of the untreated roving (5.2 grams). In two minutes this force had dropped to 17 grams and in 15 minutes it was down to about 12.5 grams. The residual or permanent cohesive force is about 11 grams. Since the untreated roving had a cohesive force of 5.2 grams, the permanent increase is about 111%.

Hereinabove, I have stressed the advantage of the invention in providing products of increased strength and spinning properties. The treatment of the invention provides many other valuable benefits. The improvements are attained without any roughening or stiffening of the textiles. There is no cell wall weakening or increase in water absorption characteristics. Dyeing properties of the products are not altered so that they may be dyed by conventional procedures. In the case of wool and mohair the important benefit is gained that the products are more shrink resistant than the untreated materials. Also, the treatment decreases the acid--and alkali-solubility of the fibers.

One form of apparatus for applying the process of the invention is illustrated in FIG. 3 in the annexed drawing. Referring thereto, the corona cell generally designated as 5 includes two plates 6 and 7 of dielectric material such as glass, separated by a small distance-about to inch. In contact with the respective plates 6 and 7 are electrodes 8 and 9, made of aluminum, copper, or other electrically-conductive material such as a resin impregnated with colloidal silver.

For energizing the corona cell there is provided a step-up transformer 10. The secondary winding of the transformer is connected to electrodes 8 and 9. (Symbols x, x in FIG. 3 represent an electrical connection omitted from the figure to avoid confusion with other parts.) The primary winding of transformer is connected to an AC power source. Center tap 1.1 of the secondary winding is preferably grounded, as shown. The parameters of the energizing system and the power source are generally chosen to provide an EMF across electrodes 8, 9 of about 10,000 to 25,000 volts at a frequency of about 60 to 5000 Hz. Energized as above set forth, a discharge takes place in the space between plates 6 and 7. Thus the space emits a diffuse violet-colored glow which appears as a series of brush discharges. The discharge causes the formation of various gaseous substances within the space between plates 6 and 7. Thus in addition to the normal constituents of air (since the space is open to the atmosphere), there is present:

Monatomic oxygen (0) Monatomic oxygen in both negatively and positively charged states Molecular oxygen (0 vibrationally excited by the visible light Molecular oxygen in both negatively and positively charged states Ozone (O Ozone, vibrationally excited by the ultraviolet light Ozone in both negatively and positively charged states Oxides of nitrogen, including nitrogen pentoxide and nitrous oxide From the above it is apparent that various reactive forms of oxygen and nitrogen are present in the discharge area. Many of the highly reactive species--for example, the vibrationally excited and charged species-decay rapidly and cannot be removed from the discharge area in a gas stream. Accordingly, direct exposure of fibrous material to the discharge area in accordance with the invention produces reactions and fiber modifications which are different from those obtained when the gaseous products of the discharge area are removed therefrom and only then applied to a fibrous material.

Referring again to FIG. 3, numeral 12 represents a casing of thermally-insulating material which surrounds cell 5 and which is provided with cut-out portions for permitting passage of the material under treament. Conduits 13 and 14 are provided so that air may be passed through the system for control of temperature. In a preferred system, air supplied by a thermostatted heat exchanger is passed through casing 12 whereby the system can be held at a predetermined temperature. In general, the corona cell can be operated in the range from about 45 to 140 C. Significant advantages are obtained when the corona cell is operated at the higher temperatures within said range, that is, above C. These advantages are that the product has greater cohesiveness, hence better spinning quality and the yarns produced from the products have increased tensile strength. Also in treating wool at the higher temperatures, one attains improved shrink resistance. Also, pilling and fuzziness are reduced when the products are subjected to washing. It is to be emphasized that these results attributable to high-temperature corona treatment are over and above the improvements attained at the lower temperatures.

As evident in FIG. 3, the space between plates 6 and 7 is open to the atmosphere and hence air can freely enter the discharge zone. Operation of the system under such conditions provides excellent results. In a preferred mode of operation, however, chlorine gasor more preferably, chlorine gas diluted with airis fed into the corona discharge zone. Thus, a mixture of air and gas from source 15 is fed into the corona cell via pipe 16. I have shown (in U.S. Patent 3,391,986) that feeding of chlorine gas into the corona cell improves shrinkproofing effect in the treatment of wool. I have now found that the use of chlorine gas provides special advantages in the treatment of cotton, particularly in increasing the cohesiveness thereof. For example, two runs on cotton were conducted under otherwise identical conditions but using air alone in one, and air plus chlorine (5 volumes to one volume) in the other. These runs provided the following results (measured 60 seconds after completion of the corona treatment): Where air alone was used the treated fibers had a cohesiveness of 7.5 grams; where air plus chlorine was used the cohesiveness of the fibers was 22 grams.

5' s (The untreated cotton had a cohesiveness of 5.2 grams.) Generally, in practicing this modification of the invention the corona cell is fed with a mixture of chlorine and air inthe' range of 'about 5ft'o'50 volumes of air per volume of chlorine.

Operation of the system: In operation, the corona cell is energized and textile material (a thin web of cotton or wool fibers, for example) from .roll 17 is continuously fed through the cell by driven rollers 18. The speed of rollers 18 is adjusted so that the fibrous material remains in the discharge zone fora period long enoughto attain the desiredmodification but not long enough to damage the fibers. This time will generally range from about 1 to about 30 seconds. Also. during operation, thermostatted air is circulated throughcasing 12 to maintain the corona cell at a temperatureof about 4 5 to 145 C.

From corona cell 5, the treated textile material is fed directlyto aconventional spinning frame, represented'by block 19, wherein the corona-treated fibers are spun into yarns by drafting and twisting operations. Since the spinning is conducted without delay' after corona treatment, one realizes the full benefit of improvement in spinning quality (i.e., both transitoryand? permanent eifects) whereby the many advantages as above explained are attained.

The invention is further demonstrated by the following illustrative examples.

Example 1 Corona treatment Yarn properties Residence Tensile Elongation Temp., time, Gas fed strength, break Run sec. to cell grams percent Control 711 7. 9 1 4950 1.4 Air 752 7.3 2 49-50 3. 2 Air 784 9. 6 3 49-50 1. 4 20% chlorine 789 7. 0

in arr. 4 93-96 1.4 Air 786 8.0 5 93-96 3.2 Air 822 7. 3 6 93-96 1. 4 chlorine 841 7. 7

in air.

The above-tabulated data shows that the 3.2-second air corona treatment produces a higher yarn tensile strength than the 1.4-second treatment at both 49-50 and at 93-96, but the increased duration of treatment is more effective at the higher temperature. At the short 1.4-second treatment times, at both 49-50 and 93-96, injecting a 20% (by volume) chlorine-air mixture into the corona cell during treatment is effective in further increasing the yarn tensile strength. At 9396, the chlorine mixture produces the largest increase in yarn tensile strength (18.3%) of all the conditions tried.

A woven fabric was constructed from the coronatreated yarn (run 6 above) and another woven fabric was constructed from the untreated yarn. The two fabrics were then tested for abrasion resistance on the Stoll flex abrasion tester. The results given below are averages of ten tests of each of the fabrics:

Product: Abrasion resistance, cycles Corona-treated fabric 1094 Untreated fabric 726 All of the yarns produced from the treated fibers were knitted into fabrics and found to have increased strength (as compared to fabrics knitted from the untreated yarns) as measured by the ball burst test.

The fabrics knitted from the treated and untreated yarns were dyed. The dyebath contained three direct (cotton) dyes-Superlitefast orange, Sol aquafast red RL, and Caledor resinfast blue, with salt, wetting agent (Igepal) and ammonium sulphate. The fabrics were agitated during dyeing in a paddle dyer for 2 hours. There was no discernable difference in shade of color of the fabrics. However, the control untreated fabric had a fuzzy surface not present in the corona-treated fabric. Also, the treated fabric had a better stitch clarity which is another important benefit in improving the washability of cellulosic fabrics. In washing, corona-treated fabrics are less fuzzy. Another advantage of corona treatment is that the resultant fabrics have a hand that is as soft as the untreated control. No harshening is imparted. A further advantage is that the treatments do not disturb the normal water repellent waxy coating of the fibers. For example, when drops of water are placed on both the treated and untreated cotton roving they remained on the surface, even after 2 hours. Water repellency is an important and valuable propertyin a fabric in inclement weather.

Example 2 That corona treatments can also improve the cohesiveness of synthetic fibers is shown in the following experiment. Polyacrylonitrile (Aorilan-l6) card batting was treated at 8898 C., 18.4 kv. at 800 hertz for 5 and 10 seconds with and without injection of a 9% chlorine-air gas mixture. The results (see following table) show that increased corona treatment time, and the addition of the chlorine gas mixture, improve the results obtained.

Treat- Single ment; fiber time, friction Fiber sec. Gas in corona cell (11) Untreated acrylic 226 Corona-treated acrylic" 5 Air 244 Do 5 9% chlorine in air- 247 Example 3 W001 roving was treated in a corona cell as described above. Conditions used were: 15 kv. at 60 Hz, residence time 31 seconds. The corona cell was supplied with ambient air, and the temperature of the cell was varied (as indicated below).

The treated roving was tested for cohesiveness 30 seconds after the corona treatment. The results are tabulated As evident from the above table, the cohesiveness of the product increases with increasing temperature. The treatment at C. yields a 230% increase in cohesiveness.

Having thus described the invention, what is claimed is:

1. A process for preparing yarns which comprises (a) exposing textile fibers to a corona discharge zone at atmospheric pressure, I

(b) continuing said exposure for a period long enough to attain an increased cohesiveness of the fibers but not long enough to damage them, and

() without any substantial delay, spinning the coronatreated fibers into yarns.

2. The process of claim 1 wherein the fibers are wool.

3. The process of claim 1 wherein the fibers are cotton.

4. The process of claim 1 wherein the spinning is applied while the fibers retain a substantial portion of the transitory increase in cohesiveness imparted to them by the corona treatment.

5. The process of claim 1 wherein the fibers are wool and wherein the fibers are spun not more than about 85 minutes after completion of the corona treatment.

6. The process of claim 1 wherein the fibers are cotton and wherein the fibers are spun not more than about minutes after completion of the corona treatment.

7. The process of claim 1 wherein a mixture of air and chlorine gas is fed into the corona discharge zone.

8. A process for improving the spinning quality and abrasion resistance of cotton fibers which comprises exposing cotton fibers to a corona discharge zone into which is fed a mixture of air and chlorine.

9. The process of 8 wherein the corona discharge zone is at essentially atmospheric pressure.

10. A process for improving the properties of cotton fibers which comprises (a) exposing cotton fibers to a corona discharge zone at atmospheric pressure, and

(b) continuing said exposure for a period long enough to attain an increased cohesiveness of the fibers but not long enough to damage them,

(0) the temperature of the corona discharge zone being at about to C.

References Cited GEORGE F. LESMES, Primary Examiner J. CANNON, Assistant Examiner US. Cl. X.R.

82, 111, 115.5, 127.5, 128 R, 129, Dig. 4, Dig. 21; 34- Dig. 24; 57 -156; 204l65, 168 

